1. Field of the Invention
The present invention relates to an improved waste incineration method and apparatus wherein successive batches of waste are substochiometrically combusted in a primary zone and then further combusted in a secondary zone with excess air to prevent the formation of smoke.
2. Brief Description of the Prior Art
Successive batch incineration methods and apparatus which utilize substochiometric combustion in a primary combustion zone followed by additional combustion with excess secondary air in a secondary combustion zone to insure complete combustion and the elimination of smoke, fumes and odors have been developed and used heretofore. While various techniques have been utilized for controlling the rates of primary and secondary air introduced into the primary and secondary combustion zones, such techniques have generally suffered from the disadvantage that the rate of secondary air is too high and overcooling of the combustion gases and secondary combustion zone take place during loading and during the time during the incineration of each batch of waste material when the secondary combustion chamber is below operating temperature. Such overcooling is uneconomical in that it wastes heat which must be replaced by the burning of extra auxiliary fuel or other means.
Incinerators including primary and secondary combustion chambers have often heretofore utilized temperature control instruments to control the rates of both the primary and secondary air. That is, a primary temperature controller senses the temperature of the combustion gases exiting the primary combustion chamber and adjusts the primary air rate accordingly to control the temperature of the combustion gases at a selected level. In a like manner, a secondary temperature controller senses the temperature of the combustion gases withdrawn from the secondary combustion chamber and adjusts the rate of secondary air to maintain the temperature of such gases at a relatively high selected temperature level. When such incinerators are being operated intermittently, i.e., time delays are incurred between batches of waste material or between groups of batches of waste material being incinerated, such high temperature level of the gases withdrawn from the secondary combustion chamber often cannot be maintained and overcooling takes place. That is, because the maximum rate and combustibility of combustion gases conducted to the secondary combustion chamber occur during the peak incineration stage of each waste batch, the temperature of the combustion gases produced in the secondary combustion chamber cannot be maintained at the selected high temperature level during the loading, initial incineration step and final incineration stage of each waste batch. Thus, when the temperature of the combustion gases produced in the secondary combustion chamber is below the selected temperature level as a result of intermittent incinerator operation and the rate and combustibility of the combustion gases conducted to the secondary combustion chamber being too low during the loading, initial incineration and final incineration stages of each waste batch, it has heretofore been the practice to simply maintain the rate of secondary air at a constant relatively high level to insure complete combustion and prevent the formation of smoke during such stages. This results in the overcooling of the combustion gases and incinerator apparatus. As mentioned, such overcooling is uneconomical in that it wastes heat. The overcooling is particularly disadvantageous where the combustion gases from the secondary combustion chamber are utilized as a heat source in a downstream system such as a steam generator or space heater.
Thus, there is a need for an improved incineration method and apparatus whereby overcooling in the secondary combustion zone which brings about the waste of heat does not take place, and the combustion gases withdrawn from the secondary combustion zone are maintained at a high overall temperature level during the incineration of each batch without the formation of smoke.